As integrated circuit (IC) design progresses, it becomes a useful expedient to integrate devices having substantial power dissipation into IC chip structures. The chip is ordinarily mounted on a heat sink structure that acts to remove the heat from the chip to prevent excessive temperature rise. If more power is dissipated than can be removed by the heat sink, the device temperature will rise. Such a rise, if not controlled, can reach a destructive level. If the input energy available is sufficiently limited and the heat sink adequate, dissipation will not cause excessive temperature rise. However, simply limiting the input energy makes it very difficult to take advantage of the useful device characteristics. For example, in a low current system high voltages can be employed with voltage break-down setting the operating limit. In a low voltage system high currents can be employed. Typically, a chart is provided for a given device to display voltage and current values. An operating line is drawn on the chart to denote the maximum power contour. The circuit designer then makes such that the maximum power contour is not exceeded. If necessary, the designer can employ limiting circuitry to ensure compliance with the power limits.
As the maximum power contour is approached, danger of exceeding it increases and conservative design means that the device characteristics cannot be fully exploited. As the maximum power contour is approached, the designer typically employs more complex limiting circuitry. It would be desirable to employ internal circuitry in IC form to provide the operating condition limits.